Stitched multi-axial reinforcement and a method of producing the same

Abstract

A stitched multi-axial reinforcement and a method of producing a stitched multi-axial reinforcement. The stitched multi-axial reinforcement ( 40 ) may be used in applications where high quality and strength is required. The stitched multi-axial reinforcement includes at least two sets of mono- or bonded multifilaments arranged transverse to one another between reinforcing layers for ensuring good resin flow properties in directions transverse to the direction of the unidirectional rovings ( 20′, 32′ ).

The invention claimed is: 
     
       1. A stitched multi-axial reinforcement for the manufacture of fiber reinforced composites by one of resin transfer molding process and vacuum infusion molding process, the stitched multi-axial reinforcement comprising:
 a first reinforcing layer of continuous unidirectional rovings having a first axial direction, 
 a second reinforcing layer of continuous unidirectional rovings having a second axial direction, wherein the first axial direction is at a non-zero angle to the second axial direction; and 
 a first set of mono- or bonded multifilaments between the first and the second reinforcing layers, 
 stitches bonding together the first and the second reinforcing layers, and the mono- or bonded multifilaments of the first set, and 
 a second set of mono- or bonded multifilaments arranged between the first and the second reinforcing layers in a direction transverse to the mono- or bonded multifilaments of the first set of mono- or bonded multifilaments, and the first set of mono- or bonded multifilaments has a diameter different than a diameter of the second set of mono- or bonded multifilaments. 
 
     
     
       2. The stitched multi-axial reinforcement as recited in  claim 1 , wherein the mono- or bonded multifilaments of the first set and mono- or bonded multifilaments of the second set are each transverse to at least one of the first and second axial directions. 
     
     
       3. The stitched multi-axial reinforcement as recited in  claim 1 , wherein the mono- or bonded multifilaments of the first set and mono- or bonded multifilaments of the second set are parallel with one of the first and second axial directions. 
     
     
       4. The stitched multi-axial reinforcement as recited in  claim 1 , wherein the mono- or bonded multifilaments of the second set extend from one edge of the stitched multi-axial reinforcement to an opposite edge of the stitched multi-axial reinforcement. 
     
     
       5. The stitched unidirectional or multi-axial reinforcement as recited in  claim 1 , wherein the mono- or bonded multifilaments of the first and the second set are arranged at an angle of at least five degrees to at least one of the first and the second axial directions. 
     
     
       6. The stitched multi-axial reinforcement as recited in  claim 1 , wherein the mono- or bonded multifilaments each have a diameter in a range of 50 μm to 2000 μm. 
     
     
       7. The stitched multi-axial reinforcement as recited in  claim 1 , wherein one of the first and second sets of mono- or bonded multifilaments has a diameter varying between 50 μm and 1000 μm. 
     
     
       8. The stitched multi-axial reinforcement as recited in  claim 1 , includes a third set of mono- or bonded multifilaments forming at least one of a top surface or a bottom surface of the stitched multi-axial reinforcement. 
     
     
       9. The stitched multi-axial reinforcement as recited in  claim 1 , wherein a spacing between the mono- or bonded multifilaments of each of the first and second sets is in a range of two mm to 50 mm. 
     
     
       10. The stitched multi-axial reinforcement as recited in  claim 1 , wherein the mono- or bonded multifilaments in at least one of the first and second sets have an aspect ratio of less than 2. 
     
     
       11. The stitched multi-axial reinforcement as recited in  claim 1 , wherein each of the stitches has a stitch length and that a distance or spacing between adjacent ones of the mono- or bonded multifilaments in the first set is longer than the stitch length. 
     
     
       12. The stitched multi-axial reinforcement as recited in  claim 1 , wherein the rovings of the first or second reinforcing layers are man-made or natural fibers. 
     
     
       13. The stitched multi-axial reinforcement as recited in  claim 1 , wherein the first and the second set of mono- or bonded multifilaments include resin flow passages adjacent sides of the mono- or bonded multifilaments. 
     
     
       14. A sandwich laminate comprising:
 a core layer, and 
 at least one of the stitched multi-axial reinforcement of  claim 1  arranged on a face of the core layer. 
 
     
     
       15. The sandwich laminate as recited in  claim 14 , wherein one of the at least one stitched multi-axial reinforcement is on a first face of the core layer and another of the at least one stitched multi-axial reinforcement is on a second face of the core layer. 
     
     
       16. The sandwich laminate as recited in  claim 14 , including an additional reinforcing layer provided in connection with the at least one stitched multi-axial reinforcements. 
     
     
       17. A method of producing a stitched multi-axial reinforcement for fiber reinforced composites comprising:
 a) laying continuous rovings unidirectionally side by side in a first axial direction to form a first reinforcing layer, 
 b) laying a first set of mono- or bonded multifilaments on the first reinforcing layer in a direction transverse to the first axial direction of the unidirectional rovings of the first reinforcing layer, 
 c) laying a second set of mono- or bonded multifilaments on the first reinforcing layer and on the first set of mono- or bonded multifilaments in a direction transverse to both the first axial direction of the mono- or bonded multifilaments of the first set and a second axial direction, 
 d) laying continuous rovings unidirectionally side by side in the second axial direction on the first reinforcing layer, and on the first set and on the second set of mono- or bonded multifilaments to form a second reinforcing layer, and 
 e) stitching the first and second reinforcing layers and the first set and the second set of mono- or bonded multifilaments therebetween to one another to form a multi-axial reinforcement with a top surface and a bottom surface, 
 wherein steps a) through c) are repeated before performing step d) to add one or more layers to the multi-axial reinforcement. 
 
     
     
       18. The method as recited in  claim 17 , wherein, before step a) laying continuous rovings unidirectionally side by side in a third axial direction to form a third reinforcing layer when producing a triaxial reinforcement. 
     
     
       19. The method as recited in  claim 18 , wherein, after step d) laying continuous rovings unidirectionally side by side in a fourth axial direction to form a fourth reinforcing layer when producing a quadraxial reinforcement. 
     
     
       20. The method as recited in  claim 17 , wherein, in steps b) and c), laying the mono- or bonded multifilaments of the first set at an angle deviating at least five degrees from the first axial direction and laying the mono- or bonded multifilaments of the second set at an angle deviating at least five degrees from the second axial direction. 
     
     
       21. The method as recited in  claim 17 , steps b) and c) include laying the mono- or bonded multifilaments of the first set and the second set such that the mono- or multifilaments of at least one set are parallel with an axial direction of the reinforcing rovings of a more remote reinforcing layer. 
     
     
       22. The method as recited in  claim 17 , further comprising providing a third set of mono- or bonded multifilaments on at least one of the top and the bottom surfaces of the multi-axial reinforcement.